Study on Sludge Reduction of A/o Process with Low C/p Ratio

Policy of energy conservation and emission reduction has been advocated during recent years in China. The development of wastewater treatment has presented some problems with a huge sludge production and high operating cost. Eutrophication occurred frequently in many water bodies of China and discharge standards for wastewater treatment plants (WTTPs) are strict with nutrient removal. However, many WWTPs in China are confronted with the problem with low influent C/P ratio resulting in poor effluent quality. In this paper, excess sludge from A/O process with low C/P ratio was treated by ultrasound and then fed back to the system for improving the cryptic growth of microorganisms and stimulating the role of denitrifying phosphate accumulating organisms (DPAOs). Batch experiments displayed that about 67% of carbon source from the treated sludge (0.25 W mL ultrasonic intensity and 10 min sonication time) could be utilized, comparing with acetate. And the results indicated about 36% sludge reduction efficiency could be achieved, in which 50% of excess sludge treated by ultrasound was recommended in order to save energy. Also, the effluent quality, especially total phosphorus, was improved since organic materials from sludge decomposition were used as carbon source for enhancing the function of DPAOs, and TP removal efficiency increased by 27%. *Corresponding author Email: [email protected] INTRODUCTION Policy of energy conservation and emission reduction has been advocated during recent years in China. Therefore, the implementation of this policy is significant in the operation and management of wastewater treatment plants (WWTPs). And the development of wastewater treatment has been nagged by the problem of huge sludge production and high operating cost. The investment and operating cost of sludge treatment and disposal may account for 2565% of the total cost of WWTPs [1,2]. In recent years, sludge ultrasonic treatment, especially about the variations of its structure, rheological and dewatering properties has been studied [3-6]. Actually, in many researches, the intracellular materials released from the treated sludge by ultrasound could be reused as substrate for microbial metabolism, and could improve microbiological cryptic growth to reduce sludge production and accelerate the process of anaerobic digestion [7-12]. The nutrient removal of WWTPs became more and more important because of the issue of eutrophication and the strict discharge standards. However, many WWTPs in China have had to be confronted with low C/P ratio of the influent and bad effluent quality [13-15]. The objectives of the paper are firstly to evaluate the possibility of the excess sludge as an alternative for carbon source, and secondly, to display how the decrease of sludge production and the improvement of effluent quality of A/O (anaerobicanoxic-oxic) process with low C/P ratio are achieved.